Phthalates, e.g. dibutyl, dioctyl or diisononyl phthalate, have been very frequently used as plasticizers for plastics such as polyvinyl chloride (PVC). However, recently, health concerns about their use have been raised, and their use in toys or other products is increasingly criticized. In some countries, their use is prohibited. It is known through long-term animal studies that phthalates may induce peroxisome proliferation, which may be the cause of liver cancer, in mice and rats. Accordingly, demand on alternative plasticizers, which are safe for humans and the environment, is on the increase.
As an alternative, di(C6-C12)alkyl cyclohexanoate-based plasticizers are evaluated as an eco-friendly and safe material without toxicity. They are obtained by first preparing phthalate plasticizers or terephthalate plasticizers and then converting them to cyclohexanes through addition of hydrogens to the benzene ring of the plasticizer. However, according to the method, since the cyclohexanoate-based plasticizer is prepared by direct hydrogenation after preparing the high-molecular-weight terephthalate plasticizer having (C6-C12)alkyl groups, the hydrogenation of the benzene ring is relatively difficult due to the steric hindrance by the long high-molecular-weight aromatic chain and the high viscosity of the reaction solution. As a result, a more vigorous reaction condition is required to solve the difficulties of the hydrogenation, which increases the risk of side reactions, including the breakage of the long carbon chain, decomposition or reduction of ester groups, etc., thereby reducing product purity. Further, since it is impossible to control an isomer of the cis/trans content of the resultant cyclohexanoate, it is difficult to selectively prepare the 60% or more cis-dimethyl cyclohexane-1,4-dicarboxylate desired by the present invention.
Korean Patent No. 10-0635396 proposes a use of cyclohexane-1,3- and -1,4-dicarboxylic acid derivatives as a plastic plasticizer, and discloses a material prepared by hydrogenation of isophthalate and terephthalate, and a preparation method thereof. However, since the above-mentioned patent describes on the hydrogenation, which is performed on terephthalate, the afore-said problem remains.